Hydrogen sulfide (H2S) gas has high acute toxicity, but little is known about the effects of long-term, low-level exposures. Current evidence indicates the nervous system, the respiratory system and the eye are the most sensitive organs to effects of H2S. Substantial chronic occupational and community exposures to H2S occur in the United States. Sources include concentrated animal feeding operations, pulp mills, and gas refineries. However, small exposed population sizes, fears caused by the "rotten eggs" odor of H2S, potential reporting biases from litigation and compensation issues, and potential confounding by other exposures have made very difficult investigations into whether health effects are caused by chronic H2S exposures. Rotorua city (population >50,000), situated on a geothermal field in New Zealand, presents a unique opportunity to investigate whether chronic H2S exposure causes health effects. No other large population exists where chronic low-level exposures to H2S, in the absence of other potentially toxic gases, coincide with acceptance of the odor as a fact of daily life (avoiding possible biases from fear-induced symptoms or pending litigation). This cross-sectional study of a sample of the Rotorua population follows earlier research suggesting possible health effects associated with H2S exposure in the city. The study sample will consist of 1,800 adults, aged 18 to 65, living in Rotorua areas with high, medium and low exposures to H2S. We will obtain: (1) responses to a questionnaire, including questions on demographic factors, symptomatology, and residential and occupational histories;(2) the results of a battery of tests of neurobehavioral function;(3) the results of an examination of peripheral nerve function;(4) the results of lung function testing by spirometry;and (5) the results of ocular and vision testing including examination for cataract and color vision impairment. Exposure data will be based on extensive Rotorua monitoring data for H2S, with spatial modeling of exposures across the city. For each participant, the information from the questionnaire on residential and work histories and daily movement patterns will be combined with the H2S modeling results to construct individual cumulative exposure indices. To validate exposure estimates, a sample of participants will wear personal H2S samplers for three weeks. Statistical analysis will seek associations between the exposure indices and each of the measures of health effect - neurobehavioral, peripheral neuropathy, respiratory and ocular function/vision. Study results will either confirm the adequacy of current U.S. occupational and environmental exposure standards for H2S or provide evidence that they are insufficiently health protective.